7.4.3 The Human Genome Project: Applications

Question 1

note

Answer 1

• The sequencing of the human genome is complete; the information provided by the sequence is being used to solve theoretical and practical problems.
  • The number of sequenced genomes of other species has increased dramatically.
  • Comparative genomics seeks to understand the functions of human genes and human diseases through comparisons with other species genomes.
  • Variations due to single nucleotide polymorphisms among individual human genomes occur and are being used to associate genes with disease and drug sensitivity.

Question 2

The Human Genome Project

Answer 2

• The Human Genome Project was completed with the
  publication of the sequence in the journal Nature in 2004.
• The Project determined the sequence of nucleotides in the DNA of humans. The coding genes of DNA are transcribed into RNA, which is then translated into protein. Proteins carry out many of the key functions of cells.
• The Human Genome Project did not identify the number of coding genes in the genome, but it provided an estimate. In the past it was thought the number of genes could be as many as 100,000. Before the time of the published sequence, the best estimate was about 30,000. The estimate has been revised to 20 to 25 thousand genes. By comparison, the genome of the nematode Caenorhabditis elegans contains about 20,000 genes.
• The number of completely sequenced genomes has grown rapidly. There are now about 400 completed sequences. Sequencing of another 1600 organisms is in progress.
• The availability of these sequences in databases such as BLAST (Basic Local Sequence Alignment Tool) has allowed the growth of comparative genomics.
• Comparative genomics takes information gained from studies of genes in other species and, through comparisons, gives clues to the identity and function of genes in humans.
• An example is work that suggests a role of the gene
  caspase-12 in Alzheimers disease in humans.
• The Human Genome Project produced a representative sequence of the human genome. Individual humans differ in the exact identity of specific nucleotides. These differences are called single nucleotide polymorphisms, or SNPs.
• The HapMap Project has catalogued the SNPs of a group of humans from different populations around the world. The many SNPs were then combined into a few haplotypes, or groupings of SNPs that typically occur together. These haplotypes quickly allow the variations of other individuals to be classified according to the HapMap catalogue.
• The HapMap database allows for two types of
  association study. Studies that look at associations between haplotypes and disease allow us to locate genes that may cause disease. Studies that look for associations between haplotypes and drug effectiveness allow physicians to more effectively prescribe drugs. This new field of study is called pharmacogenomics. It builds on the science of pharmacogenetics, in which the family history of drug effectiveness was studied.